Abstract: Experimental investigation of the combined radiation and natural convection heat transfer on wall surface sintered with open celled metal foams at different inclination angles is presented. The effects of wall inclination angle, Rayleigh number Ra* and thickness on heat transfer performance are studied. The heat transfer results for vertically placed smooth cooper plate are in good agreement with the available data in the literature to show the feasibility of the test rig. With increasing of the inclination angle under the same heat flux, the pure natural convection heat transfer coefficient and total heat transfer coefficient increase firstly to a turning point and then decrease. The maximum heat transfer performance occurs at an inclination angle between 60° and 80°. The radiation heat transfer accounts for 33%～44% of the total heat transfer. When placed vertically, the ratio of radiation heat transfer of metallic foam sintered surface in the total heat transfer is less than that of the smooth surface, and is improved with increasing of metal foam thickness. Compared to the smooth surface, the mean Nusselt numbers of combined heat transfer and pure natural convection heat transfer of vertically placed sintered surface increase by 1.52～1.98 and 1.16～1.66 times respectively. The temperature distribution on foam surface photographed by infrared camera are analyzed with image processing technique to validate the thermal radiation heat transfer calculation model based on average foam surface temperature.

Key words: Combined radiation and natural convection heat transfer, Inclination angle, Open-cell metal foams, Rayleigh number, Thickness, Diamond grinding wheel, Error compensation, Freeform surface, Mirror grinding, Precision grinding, F-Theta lens